http://www.archive.org/about/faqs.php#242
5/2006 update: If you uploaded the item and would like to replace or add to files within your item, under the current system this can be done without reuploading the entire fileset. More description may follow; meanwhile there is a walkthrough as a Word document with screenshots. Specifically to fix your items derived between 5/11-22/2006 that sound too fast in the onsite flash player (chipmunk problem), see this PDF document with screenshots.
http://www.archive.org/iathreads/post-view.php?id=61861
it is a bug that affected about 0.5% of the shows on the LMA and we are still working on fixing the straggling shows that haven't been fixed yet. thanks for flagging this one!